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31-5000727 Rev. 0
Combustion Air Inducer Pressure Switch (S18)
NF96DV series units are equipped with a dual combustion
air pressure switch (first and second stage) located on the
combustion air inducer orifice bracket. See Figure 11. The
switch is connected to the combustion air inducer housing
by means of a flexible silicone hose. It monitors negative
air pressure in the combustion air inducer housing.
The switches are a single-pole single-throw proving
switch electrically connected to the integrated control.
The purpose of the switch is to prevent burner operation
if the combustion air inducer is not operating or if the flue
becomes obstructed. On heat demand (first or second
stage) the switch senses that the combustion air inducer is
operating. It closes a circuit to the integrated control when
pressure inside the combustion air inducer decreases to a
certain set point.
Set points vary depending on unit size. See Table 6.
The pressure sensed by the switch is negative relative
to atmospheric pressure. If the flue becomes obstructed
during operation, the switch senses a loss of negative
pressure (pressure becomes more equal with atmospheric
pressure) and opens the circuit to the furnace control and
gas valve. A bleed port on the switch allows relatively
dry air in the vestibule to purge switch tubing, to prevent
condensate build up.
NOTE:
The switch is factory set and is not field adjustable.
It is a safety shut-down control in the furnace and must
not be by-passed for any reason. If switch is closed or
bypassed, the control will not initiate ignition at start up.
Figure 11. Combustion Air Pressure Switch
3/16 Terminals
Low Fire Switch
High Fire Switch
1/4" Terminals
Tap (negative - )
Tap (po)
Unit
Set Point
Low Heat
Set Point
High Heat
-070
0.50
0.81
-090
0.50
0.81
-110
0.50
0.90
Table 6. Pressure Switch Setting 0 - 4500’
Содержание GE NF96DV
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